1. Field of the Invention
The present invention relates to the field of turbomachines, in particular that of gas turbine engines such as turbojets or turboprops, and has as its object a vibration-damping device for stator parts.
2. Description of the Related Art
Aviation turbomachines consist of a plurality of movable bladed impellers, that is to say rotating disks on the periphery of which movable blades are attached in a gas flow, interacting with fixed bladed impellers forming stator vanes rings or upstream gas flow guide vane elements depending on whether a compressor or a turbine is involved. The latter may consist of assemblies in the form of ring sectors comprising several vanes each, or of single vanes, for example with variable pitch. These components are particularly sensitive parts because they must satisfy, in terms of dimensioning, imperatives of mechanical resistance to temperature and to the aerodynamic load while providing the seal for the gas stream. All of these aspects mean that these structures are statically loaded and that, because of the service life imperatives, the vibration amplitudes that they sustain must remain small.
Since the design and tuning of a turbomachine involves the coordination of several disciplines, the dimensioning process is iterative. Vibratory dimensioning is carried out in order to prevent the presence of critical modes in the operating range. The assembly is validated at the end of the design cycle by an engine test on which the vibratory amplitudes are measured. High levels sometimes appear induced either by synchronous or asynchronous forced responses; or by instabilities. The stator vanes rings or upstream guide vane elements must then be redesigned which is a particularly long and costly process.
The manufacturing objective is therefore to predict as early as possible, in the dimensioning cycle, the levels of vibratory response of the structures in order to be able to take the required corrective measures as early as possible in the design. Amongst these matters, mechanical damping is an important issue for the designers.
In order to ensure the robustness of these parts against vibratory fatigue, one solution consists in adding to the structure specific devices serving as sources of energy dissipation. For example, a damping means on the compressor movable impeller blades is known through document EP 1 253 290. It comprises a layer of viscoelastic material and a stress layer. Since the profile of the blades is in the gas flow stream, the solution proposed in this document provides for a notch to be hollowed out in the profile of the blades and for the damping means to be housed therein. The surface of the blade profiles in contact with the flow therefore does not present any irregularity and the gas flow is not disrupted. Such an arrangement requires awkward machining because of the thinness of the blade. In addition, there is a risk of introducing an imbalance between the various blades of one and the same impeller leading to an unbalance.